JPH03162973A - Correcting picture element position - Google Patents

Abstract

PURPOSE: To make writing possible with picture element matched between lines by beams by a method in which the position where a standard laser beam is turned on is detected, non-standard laser beams are turned on one by one, and a turn-on point is adjusted until it comes to the same position with the standard beam. CONSTITUTION: When beams are adjusted to conform to a standard beam, when the beams are in the range of a CCD array, the beams are turned on one by one. Next, delay is adjusted until it also begins to become a peak in an element 3. Next, a programmable delay line is used, and the correct turn-on position of a laser 41 on a CCD array element 3 is confirmed. Next, adjustment is done to move the turn-on point of the laser 41 to conform to the turn-on point of a laser 40, namely to generate the maximum energy of the laser 41 at the joint between the elements 2, 3 of an array 80. In this way, two beams are matched to make writing possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a multi-beam laser scanning device, and particularly to a multi-beam laser scanning device, and in particular, to eliminate pixel position errors caused by mechanical misalignment and electrical propagation delays between laser beams. Concerning an electronic correction method for correction.

[Prior Art] Although multiple beam laser devices can be used for a wide range of applications,
One such application is in printing equipment where a rotating polygon mirror is used to scan a light beam t across a photosensitive surface. Used in multiple laser beam printing devices, it is possible to generate more than one line of information at a time, and while maintaining the practical speed of rotating polygon mirrors, high pixel resolution, e.g. 480 pixels per inch or more, is possible. is possible. Multiple beam devices also offer other capabilities. That is, multiple beams can be used to change the shape of the effective writing spot by modulating the spots within a group of spots, or can be used to modulate the amount of light provided at each pixel location.

While the use of multi-beam laser systems has significant advantages over single-beam laser systems, in the case of multi-beam laser systems it is important that the print position (pixel position) is correctly aligned from row to row, i.e. It requires precise mechanical alignment to ensure that pixels written by one laser are properly aligned with pixels written by another laser. Multiple-beam devices employing laser arrays require positioning the laser diode on the chip with close tolerances to accurately position the pixels; It would be desirable to provide an apparatus that can be used with laser arrays where there is a possibility of significant misalignment and where the laser spot varies slightly. Additionally, the laser array chip is typically tilted to provide precise beam alignment in non-scanning directions. However, the tilting causes an offset between the beams in the scanning direction, resulting in pixel positioning problems. As used herein, mechanical misalignment refers to 1) physical variations in the position of the laser spot on the laser array, 2) mechanical variations in the laser array chip, or individual laser sources within the machine frame. misalignment,
and 3) offset 1 caused by tilting the laser array.

Another problem with multiple beam laser systems is the variation in electrical propagation delays resulting from the use of different laser exciters for each laser source.

Even though the exciter is of the same design, the elements that make up the exciter vary the pixel placement by varying the delay in turning one laser beam on and off from another. These fluctuations vary depending on the temperature and age of the laser exciter, and the pixel position varies dynamically.

Prior art electronic correction methods can correct large numbers of pixels for misalignment due to the required tilt of the laser array. Some of these electronic methods achieve sub-pixel accuracy. These devices require nanosecond resolution if high resolution, ie, 480 pixels per inch or higher, devices are planned. A clock frequency of 500 x 10611z is required for resolution up to 2 nanoseconds. Clocks and high-speed logic using the above-mentioned resolution are expensive.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electronic correction method for use with multiple beam scanning laser devices to correct errors due to electrical propagation delays as well as mechanical misalignment. be.

Another object of the invention is to provide a closed-loop electronic correction method for such errors.

Yet another object of the present invention is to provide an electronic correction method that uses relatively low clock frequencies but provides correction resolution within the nanosecond range.

Another object of the invention is to provide a correction method that is relatively insensitive to variations in the intensity of different laser beams as well as variations in laser spot size between beams.

Yet another object of the invention is to provide an electronic correction method that dynamically adapts to temperature and/or aging changes that create dynamic variations in mechanical misalignment or electrical propagation delays. That's true.

SUMMARY OF THE INVENTION The present invention eliminates serious propagation delays and machine hunting occurring in multiple beam laser beam heads by providing a closed loop correction device in which control signals are generated from laser beam energization. Concerning electronic correction of misregistration problems. The biasing point is then moved to the desired position and matched between the beams. Sub-pixel modification is accomplished at relatively low clock frequencies by using tapped or programmable delay lines.

The method of modifying pixel position includes detecting the position at which the reference laser beam is turned on and marking that position relative to the desired point. The non-reference laser beams are then turned on, one at a time, and their turn-on points are adjusted until they are in the same position as the reference beam. This allows the beam to write pixels in row-to-row alignment despite mechanical and electrical skew.

In one embodiment, the beam is aligned by detecting a turned-on point at the trailing edge of the detection element. In the second embodiment, the CCD
At the junction of the same two elements of the array, the beams are aligned by matching the total laser energy point between the beams.

In both embodiments, tapped or programmable delay lines are used to provide sub-pixel resolution.

The foregoing objects and other features and objects of the invention, as well as the manner in which they are achieved, will become more apparent with reference to the following description of embodiments of the invention in conjunction with the accompanying drawings, and the present invention itself. best understood.

[Example] Application of the present invention involves forming an image of an object on a photosensitive surface, developing the image, and then fusing said image to paper or other material. can be illustrated within the configuration of an electrophotographic machine in which prints are made. In most electrophotographic machines, the photographic process is of the transfer type, in which the photosensitive material is placed around a four-wheel drum or arranged as a belt driven by a system of rollers. In a typical transcription process,
The photosensitive material is passed beneath a fixed charge generating station, which applies a relatively uniform electrostatic charge, typically several hundred volts, across the photosensitive surface. The photoreceptor is then transported to an imaging station where it receives light from a light source. When the light source is fully activated, the photoreceptor discharges or reduces its charge to a relatively low level, whereas when the source is turned off, activated at an intermediate level, or activated for a relatively short period of time, the photoreceptor discharges or reduces its charge to a relatively low level. continues to have high voltage levels. In this way, the photosensitive dye is made to have a charge pattern corresponding to the print, shading, etc. desired to be printed on the receiving material.

The light source in electrophotographic printers often consists of a laser means whose beam is modulated by a character generator to control the power or length of time that exposes the photoconductor in a particular pixel area. In a multi-beam laser system, the character generator is one at a time.
Two beams can be modulated, so more than one row of pixels can be written at a time.

After forming the image on the photoreceptor, the image is transported to the development station of the machine where a developer material, called toner, is placed over the image. This material is in the form of a continuous powder and has a charge to deposit the powder on selected areas of the photoreceptor.

The developed image is transported from the developer to a transfer station, where a copy receiving material, usually paper, is combined with the developed image and a charge is transferred to the back side of the paper, causing the paper to be separated from the photoreceptor. Then, the 16 toner system is retained on the paper L and removed from the photoreceptor.

The remaining steps in the process are 1. Permanently fixing the toner image to the copy paper and cleaning the photoreceptor of any residual toner thereon so that it can be reused.

FIG. 1 shows a typical electrophotographic machine used to practice the present invention. The photosensitive material 10 is mounted on a drum l driven by a moving means (not shown) so as to rotate in the direction A.
installed on the surface of 1. A charge generator 12 applies a uniform charge of several hundred holes over the surface of the photoreceptor at a charging station 12'.

The charged photoreceptor is mounted in a dark box (not shown) and rotated to a printhead 13, which comprises a light beam source, such as a multi-beam laser generator.

This light source selectively exposes the charged photoreceptor in the imaging station 13' and either discharges the photoreceptor in areas desired to be developed (discharged area development method, i.e., DAD method) or A method of developing an infinite area (i.e. CAD method).

For the DAD method, the discharged areas of the photoreceptor are developed at a developer station 14' by a developer 14 which applies toner to cause the photoreceptor to have a visible image of the data. The developed image is rotated to transfer station 15' where a print sheet moving in direction B is juxtaposed with the surface of the photoreceptor. A charge opposite in polarity to the charge on the toner is placed on the back side of the print paper by the transfer charge generator 15 so that when the paper is peeled from the surface of the photoreceptor, the toner is attracted to the paper and transferred to the photoreceptor 10. away from the surface. Residual l-toner is cleaned from the photoreceptor at cleaning station 16' by cleaning device 16.

Selectively applying a beam of light to the photoreceptor 1o at the imaging station 13' includes printhead modulation means 1.
This is achieved through 7. For a semiconductor laser diode, a print head modulator is used to emit a light source for a long or short time to change the degree of radiation of the photoreceptor according to pattern data, or to generate light to increase or decrease the irradiation intensity according to pattern data. includes a power source that causes the source to emit light. In any case, the modulation occurs according to the data stored in memory 19. The data is sent to a raster buffer 18 and then to a printhead modulator.

Figure 2 shows print head 1 of the electrophotographic machine shown in Figure 1.
Fig. 3 shows the optical scanning device used in Fig. 3.

In the multiple beam arrangement shown in FIG. 2, four generally coaxial laser beams 40-43 are shown being emitted from the multiple beam laser array module 24. The four laser beams pass through a cylindrical lens 25 and are each focused on a surface 26 of a rotating polygon mirror. The beam is reflected from the rotating mirror onto the surface -12 of the photoreceptor 10 via a negative magnification spherical lens group 27, an anamorphic lens group 28, and a positive magnification spherical lens group 29. FIG. 2 shows folding mirror 80, exit window 31, scan length 32 across photoreceptor 10, and beam expansion optics 33. The light beam from each laser beam is detected by a photodetector 3.
reflective surface 34 to reflect the start of scan (SOS) signal to
is provided. A similar device may be used to generate an end of scan (EOS) signal, or a reflective surface may direct the end of the scanning light beam to the detector 35, and the same detector may be
It can be used for both S and EOS signals.

FIG. 3 shows that the laser array module 24 needs to be tilted in order to correctly position the pixels in the process direction p. At a resolution of 480 pixels per inch, the pixels are 480 pixels per inch (dimension b in Figure 3).
It is necessary to position it every 1/10th. The laser spots on array 24 need to be similarly closely spaced to position laser array 24 parallel to the process direction axis p. However, it is impractical to fabricate laser arrays to such tight tolerances.

Thus, array 24 is tilted at an angle that allows the laser spots to be separated by a distance greater than the distance b and still correctly space the pixels by the distance b between scan lines.

By doing so, the 20 laser spot is offset by a distance C in the scanning direction S. It is therefore necessary to electronically offset the start of printing in the scan direction between the laser beams by the time required to traverse the distance C to properly align pixel f1°li in the scan direction.

If laser beam 40 is selected as the reference laser, the pixels printed by laser beam 41 must be delayed by a sufficient time for laser beam 41 to traverse a distance C. Similarly, pixels printed by beam 42 need to be delayed by about twice the amount that beam 4l is delayed, and pixels printed by beam 43 need to be delayed by about three times the amount that beam 4l is delayed. A system was devised to provide this type of correction;
Prior art devices did not take into account electrical propagation delays between beams.

FIG. 4 illustrates the effect of electrical propagation delays and shows that in addition to the mechanical misalignment component, electrical propagation delays must be added to ensure that the pixels line up correctly. That is, the exact delay in the scan line 41 relative to the reference scan line 40 should take into account the mechanical error C as well as the electrical error e.

FIG. 5 is a simple block diagram of the circuitry for making the necessary modifications. A gated pixel clock signal 44 is provided to a delay line 45 to activate a laser exciter 46 to energize a laser 47 at the appropriate times.

The precise delay to laser exciter 46 is provided via delay select line 48. Similarly, other delays for other laser exciters in a multiple beam device are provided with appropriate delays to properly align each pixel along each scale scan line.

FIG. 6 shows a photodetector 3 that provides the information needed to correct electrical propagation delays as well as mechanical misalignment.
Example 5 is shown below. One of the required elements for a scan timing correction system is a device that can measure mechanical and electrical timing skew between beams. The apparatus shown in FIG. 6 includes a two-element start of scan (SOS) sensor 3 whose position is shown in FIG.
It is 5. The sensor need not be in close proximity to the photoreceptor 10, but should be located at a similar distance to where the beam is focused from the polygon mirror. A two-element sensor 35 shown in FIG. 6 is mounted perpendicular to the beam scanning direction.

In a typical timing arrangement shown in the prior art, the reference laser beam is moved across a two-element detector, such as detector 35, and a scan start pulse from the first element 50 is detected. and a second pulse from element 5l. In the second scan, the reference laser continues until element 50 is traversed.
energized and then deenergized. For a short time thereafter, the laser 1 is energized and illuminates the aligned element 51.

The amount of delay required to adapt laser 1 to the second pulse of the reference laser can thus be determined. However, this prior art method only measures mechanical misalignment between the reference and non-reference lasers;
Since the pulses are generated from an energized laser beam, electrical propagation delays are not determined. In order to measure the electrical propagation delay, it is necessary to devise a method that works from the on-time of the reference laser as well as the on-time of the non-reference laser. In that way, mechanical misalignment and electrical propagation delay can be measured together.

The two-element sensor shown in FIG. 6 is used in the present invention to detect the relative positions of different laser beams as they pass through. As explained in detail with respect to FIG. 7, delay lines are used to modify the scan start position on a sub-pixel basis. In the device of the present invention, 161 initialization is accomplished from the scan start sensor element 50.

That is, when the reference laser beam begins scanning, ie, energizes the sensor element 50, the gated control clocks are resynchronized. A reference laser, e.g. laser beam 40 in FIG. 3, is turned on before the time it reaches sensor element 50. When the reference laser beam energizes the scan start sensor element 50, a synchronization pulse is generated, which is used to gate the gated control clock. The reference laser beam 40 is turned off after the synchronization signal is generated and then turned on as soon as it leaves the trailing edge of the aligned sensor element 51.

To do this, the value of the evening lock is loaded into the down counter 64 (FIG. 8);
approximates the number of clock pulses between sensor element 50 and the trailing edge of matched sensor element 51. When the counter reaches zero, the reference laser 40 is turned on again, and if the alignment sensor is energized, a new value incremented by one over the previous value is loaded into the down counter and the process restarts. When alignment sensor 51 is activated, the one shift in the counter is again incremented by one and the process is restarted. The process is thus repeated until the aligned sensor element is no longer energized by the reference laser beam.

At the time of said deenergization, the down counter is decremented by 1 and the number of lags of clock pulses in the down counter increases as the reference laser 40 moves from the start of scan position to the trailing edge of the alignment sensor. Approximate the length of time required. At this point, the historical adjustments are complete and fine adjustments are made. That is, the programmable delay line 63 shown in FIG. 8 is similarly adjusted to provide the portion of the final clock pulse at which the alignment sensor detects the presence of the beam.

FIG. 7 shows the application of a series of pulses generated by a tapped or programmable delay line 63, thereby providing fine resolution within the time of gated clock pulses 53. can. After the temporal adjustment is complete, programmable delay line 63 is set to a minimum. When the alignment sensor is energized, the delay is incremented by one and the process continues until the alignment sensor is de-energized. In FIG. 7, matching pulse 54 is shown at tab B.
The occurrence between tap C and tap C is detected. Because a tapped delay line with a resolution of 1 or 2 nanoseconds is available, the rising edge of pulse 54 can be detected to a resolution of 1 or 2 nanoseconds, even if the resolution is greater than 480 pixels per inch. This is less than one-tenth of a pixel. In this manner, the delay time from the time the reference laser beam 40 generates the synchronization signal to the time the laser beam 40 exits the balance sensor is identified. The delay time controls writing by laser beam 40 and is loaded into the appropriate delay element, such as element 45 in FIG.

When aligning other laser beams with respect to the reference beam,
The process repeats as follows.

energizes the SOS sensor element 50 to generate an interperiod pulse 5
The reference beam is turned on so that 2 can be generated. The reference beam is then turned off and the next laser beam, laser beam 41, is turned on as it leaves aligned sensor element 51. This is accomplished by setting an approximate count in down counter 75. The matching sensor 51 is connected to the laser beam 41
When 27 is detected, the count of the down counter is incremented by one until the alignment sensor is no longer energized. At that point, the down counter is incremented by one and the programmable delay line 75 is adjusted to find the portion of the final clock cycle where the alignment sensor is no longer energized. In that way, the delay time required from the time the alignment laser beam 40 generates the synchronization signal to the time the laser beam 41 exits the alignment sensor is identified. The delay time is used to control writing by laser 41 and is loaded into the appropriate delay element of FIG.

Similarly, any other lasers in the multiple beam system are tested against the reference laser to find appropriate delay values for each beam. Since the rise of each laser beam is utilized in this method, the delay coefficient of each laser beam results in electrical and mechanical skew in the scanning direction.

FIG. 8 is a detailed block diagram of an apparatus for measuring mechanical and electrical skew with high resolution without requiring very high speed logic. FIG. 8 shows the elements for a 228 laser system, with channel 0 approximating channel 1. The only difference is what channel 0 does with the additional AND game 1.60. Since the operation of both channels is generally the same, only the operation of channel 0 will be described in detail.

There are two key elements for the operation of the device shown in FIG. First, the high resolution programmable delay line 63 allows accurate indirect time measurements. The absolute accuracy of the programmable delay line is not important because the process is a nulling type that scales the relative positions of the different beams. Second, electrical skew is included in the measurement by energizing the laser approximately when the beam has finished traversing the aligned sensor.

FIG. 8 shows a control device 61 that receives a scan start signal from element 50. Controller 61 loads a count into down counter 64 to begin the matching process. A programmable delay line 63 provides sub-pixel correction;
The global delay is passed through OR gate 65 and AND gate 60 to laser control path 66. The control circuit 66 also controls a laser exciter 6 that energizes the laser chip 69.
8. Image data 67 is received for modulation. The alignment signal from the detection element 5i is received by the beam latch (BOAS latch) 70 on the alignment sensor. Since the matched sensor signal is of extremely short duration,
A latch 70 is utilized.

FIG. 9A shows various timing events in the eighth prisoner's path. FIG. 9B is an enlarged view of the timing around the synchronization position. During the adjustment phase, the data contained in the image data 67 are all "1", and the data is
Clocked to 8 causes laser 0 to emit a beam. The control device 61 is a timing sensor and a motivation determining element for the device. It generates an rSOS PWRJ signal for each scan. The signal is input to AND gate 60. As a result, the reference laser can energize the first element of the SOS sensor 50 and is thus turned on when generating the SOS signal. The SOS signal is a synchronization signal for all devices. S.O.
The SPWR signal remains active until controller 61 detects the rise of SOS. During each scan, the G1 controlled clock signal generated by precision oscillator 71 is resynchronized upon detection of SOS. Controller 61 then generates the reset and 15J standardization signals through a logical combination of the trailing edge of SOS and the G1 controlled clock signal.

Controller 61 determines the amount of delay to set in programmable delay line 63 via a number of lines labeled CFO. Programmable delay line 63 is a fine delay mechanism that typically has a step size of 1 or 2 nanoseconds. The controller 6l also determines the required total pixel delay amount by providing the appropriate counter load value CCO to the down counter 64. Down counter 64 provides an elapsed delay for the device. When the control device 61 issues a reset command, the CCO is loaded into the down counter 64 along with the setting of the latch 70. At this time, the output latch 70 goes to a high level at 31 as shown in FIG. 9A.

Since the timing of the signals is most important around the synchronization time, an expanded view is shown in FIG. 9B. The interperiodization signal is the beginning of a timing event for the scan timing modifier and is generated by controller 61 a certain number of clock cycles after activation of the SOS signal. The synchronization signal is AN
One input to D-gate 62, which must transition when the clock signal is low. The synchronization signal remains low for several clock cycles to ensure that programmable delay line 63 is cleared and remains low. The controller 6 must ensure that the rising edge of the synchronization pulse is repeatable with respect to the falling edge of the scan start signal from scan to scan. By gating the input to a delay line, the delay line can be used to create a delay in the clock signal of more than one cycle of the clock.

FIG. 10 shows a second embodiment of the invention. A charge coupled device (CCD) array 80 is used in place of the 32 dual element start-of-scan sensor 35. array 8
0 indicates the second position at approximately the same position as the sensor element 35.
Located in the optical device shown in the figure. CCD array 80 is configured to detect the position of the laser beams relative to each other. Basically, a CCD array is a series of semiconductor elements, similar to photodiodes, which charge a capacitance associated with the elements when a beam of light strikes them. The amount of charge is determined by the energy supplied, ie the intensity of the light beam during the time it impinges on the semiconductor. The CCD array may be either one-dimensional or two-dimensional; in this embodiment, a one-dimensional CCD array 80 is used as shown in FIG. The array has an attached tracking device so that the amount of energy delivered to any particular semiconductor can be ascertained. In the array shown in FIG. 10, an N-element array is utilized.

In the method of this embodiment, the reference laser beam 40 is
It is turned on at some point while traversing the D array. For example, the reference beam 40 is detected while traversing the CCD element 3 in trajectory A as shown in FIG. Trace B shows that the energy associated with element 3 has increased by a sufficient amount, as indicated at 40', relative to the zero energy level in CCD element 2. During element 4 and beyond, the energy associated with the elements of the CCD array are all at maximum level 40'.

In this way, the CCD array 80 confirms that the reference laser beam 40 is turned on across the traverse r'l11 of the element 3. A programmable delay line as described above is then used to reposition the on point of laser beam 40;
The total energy in element 3 is therefore accurately positioned. That is, it is desirable to move the point at which the reference laser beam 40 turns on to the position shown by the trajectory C so that full energy is reached at the very beginning of the traversal of the CCD element 3. The programmable delay line is configured such that the transition (the point at which laser beam 40 turns on) is made by providing a series of pulses as shown at M-Q during the time the beam traverses element 3, at tap P of the programmable delay line. and Q. By adjusting the delay by an appropriate amount through the circuit of FIG. 5, the on point for laser beam 40 is shifted so that all the laser energy is delivered to the junction of elements 2 and 3, as shown by trace C in FIG. Positioned.

In adjusting the other beams to match the reference beam, one beam is turned on at a time when it is within range of the CCD array, and then the delay is adjusted until it too begins to peak at element 3. . For example, trace A in FIG. 10 shows the rise of laser 41 and at the same time shows that laser 41 generates a higher energy level than reference laser 40. A programmable delay line is then utilized to ascertain the exact turn-on position of laser 41 on CCD array element 3 and then move the turn-on point of laser 41 to match the turn-on point of laser 40.
That is, the adjustment 35 is made such that the maximum energy of the laser 4l is generated at the junction of the elements 2.3 of the array 80. In this way, the two beams are aligned.

One advantage of the CCD array embodiment is that if a particular laser beam is brighter or has a larger spot size than another, the total energy point remains independent of which laser beam is impinging on the CCD array. It is to be the same.

The absolute value of the energy is not measured, but rather the position where the laser spot reaches its full energy.

Since measurements are made for the laser beam on, electrical propagation delays as well as mechanical misalignment are taken into account in the positioning process.

While the invention has been illustrated and described with reference to preferred embodiments, it will be understood that changes may be made in form and detail without departing from the spirit or scope of the invention.

For example, the present invention has been described for a situation where an alignment sensor is energized by a laser beam and then incremented until the beam is no longer detected. If the eye alignment sensor fails to activate during the initial scan, the DOWN36 counter is decremented until a beam is detected.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an electrophotographic machine; Figure 2 is a diagram showing the laser array optics used in the machine shown in Figure 1; Figure 3 is tilted to properly align pixels in the process direction. Figure 4 shows a laser array with incorrect pixel alignment in the scan direction if not corrected, with the pixel alignment corrected. FIG. 5 is a block diagram illustrating a simple method for reducing pixel position errors to acceptable limits in the scan direction; FIG. Figure 7 shows the operation of a programmable delay line to achieve a high resolution device with a relatively low frequency evening lock; Figure 8 shows the use with the sensor shown in Figure 6. A block diagram of the circuit, FIGS. 9A and 9B are timing diagrams of the bow interposed in the circuit shown in FIG. 8, and FIG. 10 is a diagram showing a second embodiment of the present invention. (1 other person) Figure 4 Figure 0 Figure 7 Figure 5 Figure -584-

Claims (1)

[Claims] 1) In a method for correcting the position of a pixel in the scanning direction of a multi-beam laser scanning device, a position where a reference laser beam is turned on is detected, and the reference laser beam is adjusted so that the reference laser beam is turned on at a desired point. adjusting the position of the beam, detecting a position where a non-reference laser beam is turned on, adjusting the position of the non-reference laser beam so that it is turned on at the same position as the reference laser beam, and adjusting the position of the non-reference laser beam so that it is turned on at the same position as the reference laser beam; A method of correcting pixel position according to the invention, comprising the step of correcting effects due to mechanical and electrical skew by writing pixels generated by said reference and non-reference beams. 2) A method according to claim 1, wherein the step of detecting the position at which the reference laser beam is turned on comprises detecting the reference laser beam in an energized state across a first light detection element. scanning the reference beam to generate a reference signal, turning off the reference beam, scanning the reference beam across a second photodetecting element, and applying a first pulse from the second element to the reference beam; A method for modifying a pixel position, the method comprising the step of turning on at the timing at which the pixel is generated. 3) The method of claim 2, wherein the step of adjusting the position of the reference beam is such that the first pulse energizes the second photodetector element at its trailing edge. A method of modifying pixel position comprising the steps of: repositioning a leading edge of the first pulse to establish a reference beam time between the reference pulse and the first pulse. 4) The method according to claim 3, wherein the step of detecting the position of a non-reference beam includes generating the reference pulse by the reference beam and turning off the reference beam; a method for modifying a pixel position, the method comprising: scanning the non-reference beam across a pixel; and turning on the non-reference beam at a time that causes a non-reference pulse to be generated from the second photodetection element. . 5) A method according to claim 4, wherein the step of adjusting the position of the non-reference beam includes the step of adjusting the position of the non-reference beam such that the non-reference pulse A method for modifying pixel position comprising the steps of: repositioning a leading edge of a pixel to establish a non-reference beam time between the reference pulse and the non-reference pulse. 6) The method of claim 5, wherein the step of repositioning the leading edge of the first pulse generates a series of clock pulses gated to the reference pulse; generating the first pulse in a first scan of the reference beam; determining the number of total clock pulses between the reference pulse and the first pulse; and determining the number of total clock pulses between the reference pulse and the first pulse; incrementing the total number of clock pulses between the reference pulse and the first pulse by 1 during each successive scan, and then incrementing the number of clock pulses by 1 to produce the determined number of clock pulses; generating a series of incremental pulses of equal duration during the clock pulses following the last of the determined total clock pulses, determining the number of incremental pulses before the extinction of said first pulse, and incrementing the number of total clock pulses; A method for correcting pixel position, comprising the step of measuring the reference time by adding it to a number of pulses. 7) The method of claim 6, wherein the step of repositioning a leading edge of a non-reference pulse comprises: generating the non-reference pulse in a first scan of the non-reference beam; determining a total number of clock pulses between the reference pulse and the non-reference pulse; incrementing the number of clock pulses by 1 and then incrementing said number of total clock pulses by 1 to generate a determined total number of clock pulses, lasting for a clock pulse following the last of the total clock pulses determined in said step; generating a series of equally timed incremental pulses, determining the number of incremental pulses before the extinction of the non-reference pulse, and measuring the non-reference beam time by adding the determined total number of clock pulses to the number of incremental pulses; An apparatus for modifying a pixel position, comprising the step of: 8) The method of claim 1, wherein the step of detecting the position at which the reference laser beam is turned on comprises: scanning the reference beam in a de-energized state across a CCD array; A method for correcting a pixel position, comprising the step of: turning on the reference beam at a time when a signal is generated from the reference beam. 9) The method according to claim 8, in which the step of adjusting the position of the reference beam
A method of modifying pixel position, characterized in that this is accomplished by moving the point at which the reference beam is turned on until all laser energy is detected at the junction of the D-array elements. 10) The method according to claim 9, wherein the step of detecting the position of the non-reference beam comprises
A method for modifying pixel position comprising: scanning the non-reference beam in a de-energized state across a CD array; and turning on the non-reference beam at a time to generate a signal from the CCD array. 11) In the method according to claim 10,
The step of adjusting the position of the non-reference beam is accomplished by moving the position at which the non-reference beam is turned on until all laser energy is detected at the junction of the adjacent CCD array elements. How to fix the pixel position. 12) In the method according to claim 11,
The step of adjusting the position of the reference beam further comprises: generating a series of incremental pulses during the time that the reference laser beam traverses the CCD element just before said adjacent CCD element first detects the total laser energy of the reference beam; A method for modifying a pixel position, comprising the steps of: determining a number of incremental pulses before detecting energy; and moving a point at which the reference laser beam is turned on according to the determined number of incremental pulses. 13) In the method according to claim 12,
The means for adjusting the position of the non-reference beam further comprises detecting the total laser energy first in the CCD array element immediately after the CCD element identified in claim 12 as first detecting the total laser energy. moving the point at which the non-reference beam is turned on so as to generate a series of incremental pulses at a time when the non-reference laser beam traverses the CCD element just before the adjacent CCD element first detects the full energy of the non-reference laser beam; , determining a number of incremental pulses before detecting the total laser energy; and moving a point on of the non-reference laser beam according to the determined number of incremental pulses. Method.